Gas chromatography is a technique used for the separation of mixtures. In gas chromatography, the sample is often introduced as a liquid into the injection port whereafter it is volatilized. An inert gas is used as a carrier to propel the volatilized sample into the gas chromatographic column where the sample mixture is separated into its components. Each separated component is further propelled by the carrier gas through the exit of the gas chromatographic column into a detector. The detector then provides information regarding the amount and identity of each component of the sample mixture.
The injection port is the point at which the sample is introduced into the machine prior to separation of components. The injection port typically operates at elevated temperatures to ensure that the sample mixture is vaporized and transitions into the gas phase prior to separation entry to the chromatographic column. To assist this vaporization a disposable liner made of an inert material such as glass or quartz is placed within the injection port. A side effect of this process is that the liner also traps non-volatile components within the sample mixture. After repeated exposure to sample introductions, the injection port liner may loose its inert characteristics or become dirty and thus require replacement.
When using dirty sample matrices liner replacement is required frequently. This requires the uncoupling of two sealing surfaces to remove and replace the liner, followed by a recoupling of these sealing surfaces. This sealing is usually provided through the compression of an o-ring or ferrule around the outer diameter of the liner and positioned between the two sealing halves of the injection port body.
The normal way of forming this compression is through the use of a threaded weldment nut assembly onto an injection port body which contains a sealing bevel and metal tube to house the injection port liner. Such an arrangement is illustrated in FIG. 1. Components of the threaded nut assembly usually include gas introduction lines connected to a sealing septum to bring the carrier gas to the inlet. Once the weldment assembly is removed a liner and seal is placed into the injection port body. The threaded weldment nut is then turned onto matching threads on the injection port body producing a compression seal on an O-ring around the outer diameter of the injection port liner. This compression seal couples the liner and allows the flow of carrier gas supply through the liner into the gas chromatographic column.
The threaded weldment nut assembly often requires tools such as a wrench to rotate the nut onto the thread of the injection port body. The weldment nut is inductively heated when it is in contact with the injection port body, resulting in it often being too hot to handle (temperatures up to 350° C.). When removing the weldment nut from the injection port body it must be turned several times, often with a wrench, before it is released from the injection port body. After replacing the old liner, the threaded weldment nut is cool and thus exhibits difficulty in rethreading onto the thread of the hot injection port body. This can result in cross threading and seal leakage. Liner seals may also be damaged and leak due to torsional forces produced by rotating the weldment nut.
Additionally, this process of replacing the liner may be dangerous for operators if their hands contact the hot components of the injection port body which can easily occur when rotating the weldment nut assembly. The process of unthreading and rethreading may take several minutes to accomplish which can have deleterious effects on the system by exposing the gas chromatograph and column to air.
The present invention seeks to improve the ease and efficiency of removing and replacing the weldment assembly and on the whole making it safer for operators to use.